The error happened because EPSG:5514 is no added in spatal_ref_sys table. So you can add it using the following query.
INSERT into spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext) values ( 5514, 'EPSG', 5514, '+proj=krovak +lat_0=49.5 +lon_0=24.83333333333333 +alpha=30.28813972222222 +k=0.9999 +x_0=0 +y_0=0 +ellps=bessel +towgs84=589,76,480,0,0,0,0 +units=m +no_defs ', 'PROJCS["S-JTSK / Krovak East North",GEOGCS["S-JTSK",DATUM["System_Jednotne_Trigonometricke_Site_Katastralni",SPHEROID["Bessel 1841",6377397.155,299.1528128,AUTHORITY["EPSG","7004"]],TOWGS84[589,76,480,0,0,0,0],AUTHORITY["EPSG","6156"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4156"]],PROJECTION["Krovak"],PARAMETER["latitude_of_center",49.5],PARAMETER["longitude_of_center",24.83333333333333],PARAMETER["azimuth",30.28813972222222],PARAMETER["pseudo_standard_parallel_1",78.5],PARAMETER["scale_factor",0.9999],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["X",EAST],AXIS["Y",NORTH],AUTHORITY["EPSG","5514"]]');
Source: https://epsg.io/5514
Click on the side menu under PostGIS to see the insert query.
Check if SRID-5514 is inserted using:
SELECT * FROM spatial_ref_sys WHERE srid = 5514;
Once you have inserted it, you can then change the SRID of your geometry column using the code:
SELECT UpdateGeometrySRID('your_schema', 'table', 'geom', 5514);
You can then check the change using:
SELECT ST_SRID(geom) FROM table LIMIT 1;
select * from spatial_ref_sys where srid=5514;
? If result is empty your PostGIS does not support EPSG:5514. That projection is nasty for proj4 (projection library that PostGIS is using), read github.com/OSGeo/proj.4/issues/233.